Existing Wi-Fi systems have to share a finite resource of a given radio channel between all stations wanting to use the medium. The current standard mechanism (the Distributed Coordination Function (DCF), described further below) for sharing out this resource treats all stations as equal, regardless of whether they are access points or mobile terminals, and is “fair” in the sense of giving each station the same chance of being the next station to get a packet onto the air interface. While this mechanism is robust, it does not always provide an optimal method of sharing out the available resource. In particular, it takes no account of the following factors:                1/ There is no concept of user priority, and hence it is not possible to differentiate between users who may be expecting different classes of service.        2/ The standard mechanisms deployed in commercial access points take no account of the proportion of the available air interface resource that any given station is consuming Stations at different ranges from an access point will use different modulation rates when transmitting. For example, a station close to an access point might transmit at 54 Mbps, where one at the edge of coverage might be transmitting at only 1 Mbps. As the DCF allows them to send the same number of packets, if they send the same size packets, the edge of coverage station will be using 54 times as much airtime as the station close to the access point. This may not be the optimal use of resources.        3/ For public Wi-Fi access via private access points (as used in the Applicant's public access Wi-Fi network known as BT FON), the standard mechanisms do not take air interface usage into account in differentiating between public and private users. In this respect, presently only backhaul usage is typically taken into account, which does not have a 1:1 relationship with air interface usage. That is, the present BT WiFi network currently separates public and private Wi-Fi traffic, and offers bandwidth protection to the private users on the basis of backhaul traffic flow rates.        
Traffic control is a well known concept in computer networking. For example Linux Traffic Control ‘tc’ (see http://unixhelp.ed.ac.uk/CGI/man-cgi?tc+8) implements a mechanism for implementing traffic policing, shaping, scheduling and dropping. In 802.11 Wi-Fi networks, access to the transmission medium has been traditionally controlled using the Distributed Coordination Function (see: http://en.wikipedia.org/wiki/Distributed_Coordination_Function).
In its basic form, this mechanism attempts to make access to the medium “fair,” in the sense that each station has an equal chance of being the next one to put a packet on the air. Essentially each station is allowed to transmit the same number of packets as each of the others.
WMM QoS (a profile of the IEEE802.11e Quality of Service spec) modifies the DCF to allow for the prioritization of certain types of traffic based on a number of traffic categories: Voice, Video, Best Efforts and Background.
As described at http://en.wikipedia.org/wiki/IEEE_802.11e-2005, IEEE802.11e enhances the DCF and the point coordination function (PCF), through a new coordination function: the hybrid coordination function (HCF). Within the HCF, there are two methods of channel access, similar to those defined in the legacy 802.11 MAC: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA). Both EDCA and HCCA define Traffic Categories (TC). For example, emails could be assigned to a low priority class, and Voice over Wireless LAN (VoWLAN) could be assigned to a high priority class.
With EDCA, high-priority traffic has a higher chance of being sent than low-priority traffic: a station with high priority traffic waits a little less before it sends its packet, on average, than a station with low priority traffic. This is accomplished through the TCMA protocol, which is a variation of CSMA/CA using a shorter arbitration inter-frame space (AIFS) for higher priority packets. The exact values depend on the physical layer that is used to transmit the data. In addition, EDCA provides contention-free access to the channel for a period called a Transmit Opportunity (TXOP). A TXOP is a bounded time interval during which a station can send as many frames as possible (as long as the duration of the transmissions does not extend beyond the maximum duration of the TXOP). If a frame is too large to be transmitted in a single TXOP, it should be fragmented into smaller frames. The use of TXOPs prevents stations from sending large numbers of high priority frames in a single go at low modulation rates. Alternatively, it allows fast stations to send several frames in one go. (TXOP is set to low values for the high priority access categories.)
A TXOP time interval of 0 means it is limited to a single MAC service data unit (MSDU) or MAC management protocol data unit (MMPDU). Best effort traffic generally has a TXOP of zero, which does mean just one MSDU, but at the edge of coverage with a low modulation rate, that could be quite a lot of airtime.
The levels of priority in EDCA are called access categories (ACs). The contention window (CW) can be set according to the traffic expected in each access category, with a wider window needed for categories with heavier traffic. The CWmin and CWmax values are calculated from aCWmin and aCWmax values, respectively, that are defined for each physical layer supported by 802.11e.
In other prior art, in Li, B. J., and Soung, C. L. Proportional Fairness in Wireless LANs and Ad Hoc Networks The Chinese University of Hong Kong (available online at http://www.ie.cuhk.edu.hk/fileadmin/staff_upload/soung/Conference/C56.pdf), Li and Soung disclose a method for ensuring fairness in terms of equal airtime where they consider infrastructure WLANs in which all WSs communicate with an AP. They assume the AP maintains a separate queue for each WS so that for the downlink traffic, it can allocate different bandwidths to the queues in a flexible manner. For downlink traffic, the AP acts as the coordinator to allocate the air-time equally to the WSs. For uplink traffic scheduling they disclose either:                1. Using equal TXOP length in each WS        
A straightforward approach to implement proportional fairness for uplink traffic in a WLAN is to utilize packet bursting from WSs, as defined in 802.11e standard [11], while keeping the CWs unchanged (identical for all the WSs). The bursting lengths (i.e., TXOP lengths, expressed in “seconds”) are set as the same for all WSs to achieve equal air-time usage, independent of the WSs' individual data rates. Since 802.11 MAC implicitly provides long-term equal access probability to all the WSs, equal TXOP for all the WSs leads to equal airtime occupancy in a long term; or                2. Adjusting Initial CWs of different WSs        
It is also possible to alternatively tune the initial CWs (CWMin's) of the WSs to achieve this goal for uplink traffic. The value of CWMin's can be distributed from the AP to the WSs, since the AP knows the individual air-time used by one burst from each WS.
Thus, whilst Li and Soung teach a method for upstream air-time fairness, they do not use upstream policing. Their approach (1) using equal TxOP length cannot blend different user priorities with air-time fairness as all users get the same TxOP. Their approach (2) using varying CWmin values per station has practical limitations in terms of the rate at which it can adapt to changing load and in the generation of additional Probe Request/Response pairs which run at the lowest modulation rate, and therefore will cause additional congestion. It will also increase packet fragmentation and therefore decrease the overall efficiency of the channel usage. Moreover, adopting any upstream policing technique requires adaptation at the actual sending client device, which imposes practical implementation difficulties in terms of manufacturer adoption and compatibility with legacy devices.